This invention is directed to a method of recovering petroleum from viscous petroleum-bearing subsurface formations. More particularly, this invention is directed to a solvent recovery method for recovering petroleum from subsurface formations that are penetrated by at least one injection well and one production well which extend from the surface of the earth and into the subsurface formation containing viscous hydrocarbons.
In U.S. Pat. No. 2,968,350 there is described a method for increasing the recovery of oil from reservoirs by the use of a miscible slug of fluid of a particular size. A slug of miscible fluid of a predetermined size is injected into a well followed by a slug of normally gaseous hydrocarbons of a predetermined size. The slug of hydrocarbon gases is then followed by water. U.S. Pat. No. 3,221,813 discloses a method of recovering petroleum materials from subterranean formations containing viscous tar-like petroleum materials by thermally driving the materials from the formations. In carrying out the method, a fracture is extended through the formation to communicate with an injection and a production well and a hot gas is pumped into the fracture at a pressure that is less than the fracture to the production well. Thereafter the injection of hot gas is terminated and a vapor-free liquid capable of entraining viscous petroleum materials is pumped into the fracture. Subsequently, the injection of the vapor-free liquid is terminated and the pumping of the hot gas is resumed.
In U.S. Pat. No. 3,366,176 there is described a method of recovering high viscosity oils by conducting heat wherein a well-to-well fracture is first created and propped with a material that will not melt at steam injection temperature but will melt at temperatures between steam injection and combustion temperatures. Alternatively the fracture is propped with a material that is readily oxidizable. Steam is then injected until breakthrough occurs or oil-producing rates decline. The proppant is then melted or oxidized and steam injection or other thermal recovery methods are continued. U.S. Pat. No. 3,386,513 is directed to a method of recovering viscous crude oil from a formation having a low permeability to fluids, significant porosity and amounts of oil-in-place, existing fractures and a finite gas saturation without a useful gas drive. Light hydrocarbons in a liquid state are injected from a well into the formation without creating fractures in an amount to fill up existing fractures and then an additional amount not in excess of the gas saturation volume of the formation within the wells' drainage radius exposed to the hydrocarbons. The well is shut in until the borehole pressure decline ceases. Thereafter the light hydrocarbons are produced with oil, in a liquid state, from the well.
In U.S. Pat. No. 4,004,636 there is described a method of recovering petroleum from viscous petroleum-containing formations including tar sand deposits by injecting into the formation a multicomponent solvent for the petroleum and a thermal fluid. In U.S. Pat. No. 4,109,720 petroleum is recovered from viscous petroleum-containing formations by injecting into the formation a solvent which is liquid at the formation conditions and simultaneously therewith injecting a substance which remains totally gaseous at the pressure and temperature conditions existing within the reservoir. In U.S. Pat. No. 4,124,072 there is described a method for treating a high permeability communication channel between wells for use in a viscous oil recovery method to stabilize fine particulate matter present in the communication channel to prevent movement of fine particles during the oil recovery process. U.S. Pat. No. 3,954,139 is directed to a method of recovering oil by injecting a miscible fluid to drive the oil vertically downward to the producing wells wherein the injected miscible fluid is heated so that it has a temperature equal to or greater than the normal reservoir fluid temperature.